$ -->user working prompt
Basic commands
1. logname -it displays the current user name
2. $pwd --it displays current working directory
3 $clear --it clear the screen
4. $exit – to logout from current user
5. $date – it displays system date and time
Sat mar 4 04:40:10 IST 2005
6. $ who am I – it displays current user name, terminal number, date and time at which
You logged into the system
Tecno ty01 mar 4 09:30
7. $who –To displays the information about all the users who have logged into the system
currently. Ie., each user login name, terminal number, date and time when the
person logged in
tecno1 tty01 mar 4 09:30
tecno2 tty05 mar 4 10:10
tecno3 tty06 mar 4 10:15
ie. Tecno1 – logname
tty01 - terminal name
mar 4 - date
09:30 -time
8. $finger – it displays complete information about all the users who are logged in
9. $cal – it displays previous month, current month and next month calendar
10. $cal year – it displays the given year calendar
Eg: $cal 2005 --it takes year from 1 t0 9999
11. $cal month year – it displays the given month calendar only
12. #init --to change system run levels
i. #init 0 -to shutdown the system
ii. #init 1 – to bring the system to single user mode
iii. #init 2 –to bring the system to multi user mode with no resource shared.
iv. #init 3 –to bring the system multi user mode with resource shared
v. #init 6 – halt and reboot the system to the default run level.
13. $banner “Bayon” – it prints a message in large letters
Creating files
There are two commands to create files 1. touch and cat
1. touch filename - it creates zero byte file size
Eg: $ touch sample
The size of sample file is zero bytes. Touch does not allow you store anything in a file. It is used for to create several empty files quickly.
Eg: $ touch file1 file2 file3 file4 file5
2. cat command
Syntax
i. $ cat >filename
e.g: $cat >sample
----------------
----------------
----------------
Ctrl+d (to close a file)
ii. $ cat >> sample --to append data to the file
----------------
----------------
----------------
Ctrl+d
iii. $cat file1 file2 file3 >file4
this would create file4 which contains contents of file1 followed by file2 and
followed by that of file3. ie., it concatenates file1, file2 and file3 contents and
redirects to file4. if file4 already contains something it would be over written.
3. $ cat <filename or $cat filename --to open a file
e.g: $cat sample --it displays sample file contents
e.g: $cat file1 file2 file3
-it displays file1 contents followed by file2 then followed by file3.
Removing files
4. rm command -to remove the given file
Syntax: $rm filename
$rm sample -it removes sample file
$rm –i filename -it asks confirmation before deleting the file.
$rm – sample
Remove sample? y –it removes
N – it wont remove
$rm file1 file2 file3 -it removes three files
$rm * -it removes all files in current directory
Creating directory
5. mkdir command -to make directory
Syntax: $mkdir directory name
e.g: mkdir tecno
creating multiple directories
$mkdir dir1 dir2 dir3 …dirn
Change directory
Syntax : $cd directory name
$cd tecnosoft
$pwd
/usr/tecno/tecnosoft
$cd .. –to change into parent directory
$cd\ -to change to root directory
Remove directory
1. $rmdir directory name -to delete a directory but directory should be empty
2. $rm –r directory name – it removes all files and sub directories, sub directory files
Including directory.
Shell Programs
- write a prg to display list of files, the current working user’s list and present working directory.
Vi sp1
Ls –x
Who
Pwd
:wq (save and quit)
Execution of shell program:
Sh is the command to execute bourne shell programs
Eq: $sh sp1
Or
$chmod 744 sp1
$sp1
Write program to display address
Vi sp2
Echo “ Patni Computer Systems”
Echo “Patni Knowledge park”
Echo “Navi Mumbai”
Echo “Phone :123456”
:wq (save and quit)
Write a prg count no. of users are currently logged into the system
Vi sp3
Echo “There are ‘who| wc – l’ users”
:wq (save and quit)
4. write a prg read name and display
Vi sp4
Echo “What is your name?”
Read name
Echo “hello $name”
:wq (save and quit)
Note: read is command to read variable value from the user. Read command reads value from keyboard upto space or enter key.
Eg 1: read a
Eg 2: read a b c
5. write a prg read two numbers and display
Vi sp5
Echo “entere 2 numbers:\c”
Read a b
Echo “your numbers are $a and $b
:wq (save and quit)
Operators
1. Arithmetic operators
| Operator | Meaning |
| + | Addition |
| - | Subtraction |
| * | Multiplication |
| / | Division |
| % | Modulus Division |
2. Relational operators
i. Numeric comparison operators
| Operator | Meaning |
| -gt | Greate than |
| -ge | Greater than or equal to |
| -lt | Less than |
| -le | Less than or equal to |
| -eq | Equal to |
| -ne | Not equal to |
ii. String comparison operators
| Operator | Meaning |
| > | Greater than |
| < | Less than |
| = | Equal to |
| != | Not equal to |
3. Logical operators
| Operator | Meaning |
| -a | Logical AND |
| -o | Logical OR |
| ! | Logical NOT |
6. Write a prg to read 2 numbers and display sum, difference, product and division
Vi sp6
Echo “Enter 2 numbers”
Read a b
C=’expr $a+$b’
Echo “a+b=$c”
C=’expr $a-$b’
Echo “a-b=$c”
C=’expr $a\*$b’
Echo “a*b=$a
C=’expr $a/$b’
Echo a/b=$c”
:wq (save and quit)
Note: expr is the command to evaluating arithmetic expressions. But expr is capable of carrying out only integer arithmetic
7. Write a prg to read 2 float numbers and display sum, difference, product and division
Vi sp7
Echo “Enter 2 float numbers”
Read a b
C=’echo $a+$b| bc’
Echo “a + b=$c”
C=’echo $a-$b|bc’
Echo “a-b=$c”
C=’echo $a\*$b|bc’
Echo “a*b=$a”
C=’echo $a/$b|c’
Echo “a/b=$c”
:wq (save and quit)
Control statements
There are 4 types of control instructions in shell. They are
i. sequence control instruction
ii. selection or decision control instruction
iii. repetition or loop control instruction
iv. case control instruction
The sequence control instruction ensures that the instructions are executed in the same order in which they appear in the program. Decision and case control instructions allow the computer to take a decision as to which instruction is to be executed next. The loop control instruction helps computer to execute a group of statements repeatedly.
Decision control statement
i. if – then – fi statement
syntax:
if control command
…....................
…………….
Fi
The if statement of unix is concerned with the exit status of a command. The exit status indicates whether the command was executed successfully or not. The exit status of a command is 0 if it has been executed successfully, 1 otherwise.
8. write prg to change directory
Vi sp8
Echo “Enter directory name”
Read dname
If cd $dname
Then
Echo “Changed to $dname”
Pwd
Fi
:wq (save and quit)
ii. if – then – else – fi statement
syntax:
if condition
then
----------
----------
Else
-----------
-----------
Fi
The exit status of the control command is 0 then it executes then statements otherwise it executes else statements.
9. write a prg to copy a file
Vi sp9
Echo “Enter source filename and target file name
Read src trg
If cp $src $trg
Then
Echo “file copied successfully”
Else
Echo “Failed to copy the file”
Fi
10. write a prg to search string in a file
Vi sp10
Echo “Enter file name”
Read fname
Echo “Enter to string to search”
Read str
If grep $str $fname
Then
Echo “$str is found in the file $file”
Else
Echo “$str is not found in $fname”
Fi
:wq (save and quit)
11. write prg find greatest number of 2 numbers
Vi sp11
Echo “Enter two numbers”
Read a b
If [$a –gt $b] then
Echo $a is the greatest value
Else
Echo $b is the greatest value
Fi
:wq (save and quit)
12. Write a prg to check given no. is even or odd
Vi sp12
Echo Enter a number
Read n
If [‘expr $n%2 –eq 0]
Then
Echo $n is even number
Else echo $n is odd number
Fi
:wq (save and quit)
The Test command
If constructs depends upon whether of not the condition results into true or not. If constructs are generally used in conjuction with the test command. The test command helps us to find the contents of a variable, the number of variables and the type of file or kind of file permission. The test command returns an exit status after evaluating the condition.
Syntax:
If test condition
Then
<commands>
Else
<commnands>
Fi
13. write a prg to check how many users working on the system
Vi sp13
Total=’who| wc –l’
If test $total –eq 1
Then
Echo “You are the only user working…”
Else
Echo “There are $total users working…”
Fi
:wq (save and quit)
14. Write a prg to check given number is +ve or –ve number
Vi sp14
Echo “enter a number”
Read num
If test $num –gt 0
Then
Echo “$num is +ve number”
Else
Echo “$num is –ve number”
Fi
:wq (save and quit)
15. write a prg to find student result
Vi sp15
Echo “Enter three subject marks:”
Read m1 m2, m3
If [$m1 –gt 40]
Then
If [$m2 –gt 40]
Then
If [m3 –gt 40]
Then
Echo “PASS”
Else
Echo “FAIL”
Fi
Else
Echo “FAIL”
Fi
Else
Echo “FAIL”
Fi
:wq (save and quit)
16. write a prg to print greeting
Vi sp16
Hour = ‘date|cut –c 12,13’
If [$hour –ge 0 –a $hour –le 11]
Then
Echo “Good Morning…”
Else
If [hour –ge 12 –a $hour –le 17]
Then
Echo “Good Afternoon…”
Else
Echo “Good Evening…”
Fi
Fi
:wq (save and quit)
File test commands
The test command has several options for checking the status of file
| Option | Meaning |
| -s file | True if the file exists and has a size greater than 0 |
| -f file | True if the file exists and is not a directory |
| -d file | True if the file exists and is directory file |
| -c file | True if the file exists and is character special file |
| -b file | True if the file exists and is a block special file |
| -r file | True if the file exists and you have a read permission to it |
| -d file | True if the file exists and you have a write permission to it |
| -x file | True if the file exists and you have a execute permission to it |
17. write a prg to check for ordinary file and display it contents
Vi sp17
Echo “Enter a file name”
Read fname
If test –f $fname
Then
Cat $fname
Else
Echo “given file is not ordinary file”
Fi
:wq (save and quit)
iii. if – then – elif – fi statement
18. w a p to check given file is ordinary or directory file
Vi sp18
Echo “Enter a file name: “
Read fname
If [-f $fname]
Then
Cat $fname
Elif [-d $fname]
Then
Ls
Else
Echo $fname is not file and not a directory
Fi
:wq (save and quit)
19. write a prg to check read permission
Vi sp19
Echo “Enter a file name”
Read fname
If [-r $fname]
Cat $fname
Else
Chmod u+r $fname
Cat $fname
Fi
:wq (save and quit)
20. write a prg to append data to the file
Vi sp20
Echo “enter a filename”
Read $fname
If [-f $fname]
Then
If [-w $fname]
Then
Echo “Enter data to file to stop press ctrl+d…”
Cat >>$fname
Else
Chmod u+w $fname
Echo “enter data to file to stop press ctrl+d…”
Cat >>$fname
Fi
Else
Echo “Enter data to file to stop press ctrl+d…”
Cat >>$fname
Fi
:wq (save and quit)
String test commands
| Condition | Meaning |
| String1 = String2 | True if the strings are same |
| String1 != String2 | True if the strings are different |
| -n String1 | True if the length of string is greater than 0 |
| -z string | True if the length of the string is zero |
21. Write a prg to compare two strings
Vi sp21
Echo “Enter first string:”
Read str1
Echo “Enter second string:”
Read str2
If test $str1 = str2
Then
Echo “Both strings are equal”
Else
Echo “Strings are not equal”
Fi
:wq (save and quit)
22. Write a prg check given string is empty or not.
Vi sp22
Echo “Enter a string”
Read str
If [-z $str]
Then
Echo “String is empty”
Else
Echo “Given string is not empty”
Fi
:wq (save and quit)
iv. case – esac statement
syntax
case value in
choice 1)
----------
----------
;;
Choice 2)
---------
---------
;;
:
:
Choice n
--------
--------
*)
--------
----------
;;
Esac
Firstly, the expression following the case key work is evaluated. The value the it yields is then matched, one by one against the potential choices (choice1, choice2 and choice 3 in the above form). When a match is found, the shell executes all commands in that case up to ;;. These pair of semicolons placed at the end of each choice are necessary.
23. Sample program for case
vi sp23
echo “enter a number b/n 1 to 4 “\c”
read num
case $num in
1) echo “you entered 1”
;;
2) echo “you entered 2”
;;
3) echo “you entered 3”
;;
4)echo “you entered 4”
;;
*) echo “invalid number. Enter number b/n 1 to 4 only”
;;
esac
: wq (save and quit)
24. Write a prg to check given character is upper case alphabe or lower case alphabet or digit or special character
Vi sp24
Echo “enter a single character”
Read ch
Case $ch in
[a-z] echo “you entered a small case alphabet”
;;
[A-Z] echo “you entered a upper case of alphabet”
;;
[0-9] echo “you entered a digit”
;;
?) echo “you entered a special character”
;;
*) echo “you entered more than one character”
;;
Esac
:wq (save and quit)
25. write a prg to display file contents of write on to file or execute based on user choice
Vi sp25
Echo “enter a file name:\c”
Read fname
Echo “Main menu”
Echo “-------------“
Echo “r.read mode”
Echo “w. write mode”
Echo “x.execute mode”
Echo “enter mode:\c”
Read mode
Case $mode in
r)
if [-f $fname –a –r $fname] then
cat $fname
fi
;;
w)
if [-f $fname –a –w $fname] then
echo “Enter data to file at end press ctrl+d : “
cat >fname
fi
;;
x)
if [-f $fname –a –x$fname] then
chmode u+x $fname
$fname
Fi
;;
*) echo “you entered invalid mode …”
;;
Esac
:wq (save and quit)
26. write a menu driven prg which has following options:
i. contents of current directory
ii. list of users who have currently logged in
iii. present working directory
iv. calendar
v. exit
vi sp26
echo “main menu”
echo “----------“
echo “1. list of files”
echo “2. list of users”
echo “3. present working directory”
echo “4. display calendar”
echo “5. exit”
echo “enter your choice :\c”
read choice
case $choice in
1)ls –x
;;
2) who
;;
3) pwd
;;
4) echo “Enter month and year”
Read m y
Cal $m $y
;;
5) banner “Thank you”
Sleep 1
Exit 0 --to terminate execution of shell program
;;
*) echo “Choice is wrong try again!!!”
;;
Esac
:wq (save and quit)
Looping control statements
A loop involves repeating some portion of the program either a specified no of times of times or until a particular condition is being satisfied. There are three methods by way of which we can repeat a part of a program. There are
1. Using while statement
2. Using Until statement
3. Using a for statement
I) While statement
Syntax
While [condition]
do
-------
-------
done
The statements within the while loop would keep on getting executed till the condition is true. When the condition is false, the control transfers to after done statement.
27. write a prg display numbers 1 to 10
vi sp27
echo “The numbers from 1 to 10 are:”
i=1
while [$i –le 10]
do
echo $i
i= ‘expr $i +1’
done
28. write a prg copy file from root to user directory
Vi sp28
Flag=1
while[$flag –eq 1]
do
Echo “enter a file name:\c”
Read fname
Cp $fname/usr/patni/$fname
Echo “$fname copied…”
Echo “do u wish to continue [1 –yes/0 –n0]:”
Read flag
Done
:wq (save and quit)
The break statement
When the key word break is encountered inside any loop, control automatically passes to the first statement after the loop
The continue statement
When the keyword continue is encountered inside any loop, control automatically passes to the beginning of the loop
29. write a prg display file contents if file existing
Vi sp29
X=0
While test $x=0
Do
Echo “enter a file name:\c”
Read fname
If test! –f $fname
Then
Echo “$fname is not found…”
Continue
Else
Break
Fi
Done
Cat $fname|more
:wq (save and quit)
The until loop
Syntax:
Until [condition]
Do
-------
-------
Done
The statements within the until loop keep on getting executed till the condition is false. When the condition is true the control transfers to after done statement
30. write a prg print numbers 1 to10
vi sp30
i=1
until [$i – gt 10]
do
echo $i
i=’expr $i +1’
done
:wq (save and quit)
The True and False command
To execute the loop an infinite no. of times
31. Write sample prg for True command.
Vi sp31
While true
Do
Clear
Banner “Hello”
Sleep 1
Clear
Banner “Bayon”
Sleep 1
Done
:wq (save and quit)
Note – The above prg executes continuous to stop execution press ctrl+break
32. write a prg for false command
Vi sp32
Until false
Do
Clear
Banner “Hello”
Sleep 1
Clear
Banner “Bayon”
Sleep 1
Done
:wq (save and quit)
The Sleep command
The sleep command stops the execution of the program the specified no. of seconds.
The For loop
Syntax
For variable in value1 value2 value3…valuen
Do
--------
--------
Done
The for allows us to specify a list of values which the variable in the loop can take. The loop is then executed for each value mentioned in the list.
33. Write a program to demonstrate for loop
vi sp33
for I in 1 2 3 4 5
do
echo $i
done
:wq (save and quit)
34.
for i in Patni Computers system ltd.,
do
echo $i
done
:wq (save and quit)
35. write a prg to display all files in current directory
Vi 35
For I in *
Do
If test –f $i –a –r $i
Then
Cat $i| more
Sleep 1
Clear
Fi
Done
:wq (save and quit)
36. write a prg to display all sub-directories in the current directory
Vi sp36
For I in *
Do
If [-d $i]
Then
Echo $i
Fi
Done
:wq (save and quit)
Positional parameters
When the arguments are passed with the command line, shell puts each word on the command line into special variables. For this, the shell uses something called as ‘Positional parameters’. These can be thought of as variables defined by the shell. They are nine number, named $1 through $9
Consider the following statement, where sp37 is any executable shell script file and the remaining are the arguments. $sp37 Technosoft solutions is a computer training and development institute. On entering such command, each word is automatically stored serially in the positional parameters. Thus, #0 would be assigned sp37, s$1 would be assigned “Technosoft”, $2 “solutions”, $3 is “is” and so on, till institute “,” which is assigned to $9
37. write a prg to copy a file using positional parameters
Vi sp37
if cp $1 $2
then
echo “File copied successfully “
else
echo “Failed to copy”
fi
:wq (save and quit)
$chmod 744 sp37
$sp37 a1 a2
In above command it passes a1 to $1 and a2 into $2, then it copies a1 contents to a2
S* - contains entire string of arguments
S# - contains the no. for arguments specified in the command.
% !! (recall last command)
% !-3 (recall third most recent command)
% !5 (recall 5th command in list)
% !grep (recall last command starting with grep)
% cp science.txt tempfile.txt
% ls (to check if it has created the file)
% rm tempfile.txt
% ls (to check if it has deleted the file)
